Hydraulics

Question 1

What components are driven by hydraulic system 1?

Answer 1

Brakes (outboard)
Rudder
Ailerons (both)
Thrust reversers 
Spoilers (inboard)

Landing gear
Steering
Main door

Question 2

What components are driven by hydraulic system 2?

Answer 2

Brakes (inboard)
Rudder
Ailerons (both)
Thrust reversers 
Spoilers (outboards)

Emergency brakes

Question 3

What type of hydraulic fluid is used in the ERJ-145?

Answer 3

Skydrol.

Question 4

What are some important properties of hydraulic fluid?

Answer 4

It must be incompressible.
Have a high flash point.
It’s caustic (skin irritation).
Coloured purple.

Question 5

Regarding the hydraulic system, what precautions should we be aware of?

Answer 5

It is susceptible to moisture.

It should not leak (as may be permissible on other aircraft)?

Question 6

How is the hydraulic system pressurised?

Answer 6

Each system is equipped with an engine driven hydraulic pump and an electrical hydraulic pump.
In normal operations, the engine driven hydraulic pump supplies pressure in each system.

Question 7

What fluid flow pressure is associated with the engine driven hydraulic pump?

Answer 7

3000 psi.

Question 8

What fluid flow pressure is associated with the electric hydraulic pump?

Answer 8

2900 psi.

The flow volume is about 10 times less than the engine driven hydraulic pump.

Question 9

What type of pump is the engine driven hydraulic pump?

Answer 9

Variable displacement pump.

Varies output based on system demands and engine RPM.

Question 10

What type of pump is the electric hydraulic pump?

Answer 10

Centrifugal pump.

Provides constant pressure regardless of system demands.

Question 11

What is the purpose of the hydraulic accumulator?

Answer 11

To store hydraulic pressure and absorb shocks.

Question 12

How does the hydraulic accumulator operate?

Answer 12

A flexible rubber diaphragm inside a metal canister separates a chamber filled with Nitrogen gas and the hydraulic fluid. As the system pressurises it pushes against the diaphragm.

Question 13

How many accumulators are installed on the ERJ-145, what do the supply stored energy for and where are they located?

Answer 13

One per system.
Accumulator one is for the landing gear - located in the forward right hydraulic bay (inspectable on pre-flight)
Accumulator two is for the emergency brake - located in the right side of the fuselage.

Question 14

How much energy is stored in accumulator 2 under normal circumstances (i.e. what does it guarantee)?

Answer 14

Emergency brake for 24 hours or 6 applications.

Question 15

What is the purpose of the hydraulic reservoir?

Answer 15

It stores hydraulic fluid under pressure to prevent cavitation (space forming).

Question 16

When does the automation activate the electric hydraulic pump?

Answer 16

When N2 for the associated engine falls below 56.4% or the system pressure falls below 1600 psi downstream of the engine driven pump.
If N2 or pressure is restored the pump is switched off.

Question 17

At take-off, what should we be aware of if hydraulic system 1 isn’t fully pressurised?

Answer 17

Slow landing gear retraction.

Question 18

What does the hydraulic priority valve do?

Answer 18

It is on system 1 and if the system is operating on the electric hydraulic pump, it restricts flow (to a minimum) to the gear to prioritise the flight controls.
The accumulator will provide pressure for retraction.

Question 19

How is the hydraulic system shut off valve activated?

Answer 19

By activation of the overhead panel button.
By pulling the T handle.
Powered by the hot bus.

Question 20

When would the EICAS provide a hydraulic system overheat caution message?

Answer 20

If the fluid temperature exceeds 90°C.

Question 21

When would the EICAS provide a low hydraulic fluid advisory message?

Answer 21

When the reservoir drains to below one litre.

Question 22

What powers the electric hydraulic pumps?

Answer 22

The cross side DC Buses.
Pump 2 - DC Bus 1
Pump 1 - DC Bus 2